The present invention relates to improvements in insulated doors, building panels and the like, and more particularly to an improved insulated panel for cold storage compartments.
Because of their extremely low thermal conductivity at low temperatures foamed plastic resins are superior materials for insulating cold-storage wall panels. The best and most widely used of these plastic insulants for the stated purpose is polyurethane foam. These materials, however, have the serious disadvantage of disintegrating when subjected to high temperatures. Some, like polyurethane foam, are flammable and produce toxic fumes when ignited. Where fire safety is an important factor, a panel insulated with polyurethane foam requires a supplemental fire-resistant panel to provide first protection and meet code and insurance requirements.
The present invention fulfills a pressing need for a single panel having the combined properties of a fire door and an efficient cold storage door, dual qualities which heretofore have not been obtainable in a unitary cold storage door or panel.